1. Field of the Invention
Example embodiments of the present invention relate to an optical element holder and a projection exposure apparatus having the same. More particularly, example embodiments of the present invention relate to an optical element holder for receiving a plurality of optical elements to form light having different shapes, and a projection exposure apparatus for transcribing a reticle image pattern onto a substrate using the optical element holder.
2. Description of the Related Art
In general, a semiconductor device may be manufactured by performing a fabrication process to form electrical circuits on a semiconductor substrate, an electrical die sorting process to inspect electrical characteristics of the electric circuits formed on the semiconductor substrate, a packaging process to package semiconductor devices formed on the semiconductor substrate with epoxy resins, and sorting the individual semiconductor devices.
A fabrication process may include repeating various unit processes performed in order to form electrical circuits on a semiconductor substrate. The unit processes may include a deposition process, a photolithography process, an etching process, a chemical mechanical polishing (CMP) process, an ion implantation process, a cleaning process, and the likes.
A photolithography process may be performed to form a photoresist pattern on a layer formed by a deposition process. The photoresist pattern may be used as an etching mask in an etching process performed to form a layer into desired patterns.
Further, the photolithography process may include a photoresist coating process to form a photoresist film on a semiconductor substrate, a baking process to harden the photoresist film, and exposure and developing processes to form the photoresist film into a photoresist pattern corresponding to a reticle image pattern.
As a packing density of a semiconductor device has become highly integrated, a size of patterns to be formed on a semiconductor substrate has been reduced, and thus, resolution and depth of focus (DOF) have become more important in a photolithography process.
The resolution and the DOF may be influenced by a wavelength of light beam and a numerical aperture (NA) of a projection lens. Examples of the light beam used in a photolithography process may include a G-line light beam having a wavelength of 436 nm, an I-line light beam having a wavelength of 365 nm, a KrF laser beam having a wavelength of 248 nm, an ArF laser beam having a wavelength of 193 nm, a F2 laser beam having a wavelength of 157 nm, and the likes.
Methods of preventing distortion of a photoresist pattern, for example, due to scattering and diffraction of light beam transmitted through a reticle image pattern, include using a phase shift mask (PSM) or an optical proximity correction (OPC) method.
Increasing a numerical aperture of a projection lens to improve resolution may cause DOF to deteriorate. An off-axis illumination (OAI) may be used to improve the DOF by projecting zero-order and positive first-order diffracted light beams from an image pattern onto a semiconductor substrate.
Examples of the OAI may include an annular illumination, a dipole illumination, quadrupole illumination, a cross-pole illumination, a hexapole illumination, and the like.
An exposure apparatus may include an aperture diaphragm plate to form illumination light having different shapes from each other. The aperture diaphragm plate may serve as an optical element holder to support a plurality of aperture diaphragms having different shapes from each other in order to selectively form illumination light having different shapes from each other. The aperture diaphragms may be arranged in a circumferential direction of the aperture diaphragm plate that may be rotatably disposed to select one of the aperture diaphragms. For example, the aperture diaphragm plate may have circular diaphragms to form circular illumination light having different diameters from each other, a quadrupole diaphragm for forming a quadrupole illumination light, and an annular diaphragm for forming an annular illumination light.
As shapes of a pattern have become more dynamic and a width of a pattern has become finer, there has been a need for various types of illumination light. However, increasing the number of aperture diaphragms may be limited because of design space limitations of an exposure apparatus. Therefore, it may be inconvenient to frequently change the aperture diaphragm plate, thereby deteriorating throughput of an exposure process.